OUR PURPOSE PIONEERING SCIENCE PATIENTS OUR PEOPLE ENVIRONMENT COMMUNITY REPORTING 10 CEO LETTER BIOGEN 2021 YEAR IN REVIEW erythematosus (CLE), with BIIB059. Lupus is a therapeutic area with a different risk profile, and we are continuing to evaluate additional opportunities across specialized immunology. The third pillar is biosimilars, which contributed revenue of $831.1 million in 2021. Our goal is to bring more biosimilar products to more patients across geographies, supporting the sustainability of healthcare systems and accessibility for all. To that end, we announced in January 2022 an agreement with Samsung Biologics Co., Ltd. (Samsung Biologics) to sell our equity stake in the Samsung Bioepis Co., Ltd. (Samsung Bioepis) joint venture to Samsung Biologics. This positions us to pursue further biosimilars opportunities in order to provide patient access to biologic medicines and to contribute to healthcare sustainability. With the closing of this transaction, we will retain our current role as the commercialization partner for the Samsung Bioepis anti-TNF portfolio and ophthalmology programs. Lastly, our fourth pillar is directed at accelerating our efforts in digital health. We aim to leverage our significant database and utilize machine learning and artificial intelligence to develop digital health solutions that may improve patient care, accelerate drug development, and further the understanding of underlying pathologies. In summary, we expect executing on our four strategic pillars will create the opportunity for future growth and value creation. Focused on Execution in 2022 Our focus in 2022 will remain on execution and agility as we expect a number of important milestones. This includes maintaining leadership in our core business, the launch of VUMERITY in the EU, and our expected entry into the U.S. biosimilars market with BYOOVIZ, a biosimilar referencing LUCENTIS®. In the light of the recent decision of CMS to limit coverage for ADUHELM in the U.S., we will be reevaluating certain elements of our infrastructure and reprioritizing our capital allocation in the interest of creating long-term value for our shareholders. As a research-driven biotechnology company, we continue to be centered on delivering therapies at the cutting edge of innovation. We believe we have unique capabilities and experience to leverage progress in neuroscience, technology and biology. In scientific discovery and development, we know the road is not always linear, but I believe we have the best people across Biogen to advance science and access in the pursuit of helping patients and society. I want to thank all my colleagues who work tirelessly to make Biogen such a special company and uphold the highest standards of ethics and integrity. I also want to extend thanks to our collaborators for their essential contributions, and to our investors who entrust us with their capital, which makes everything we do possible. Sincerely, Michel Vounatsos Chief Executive Officer of Biogen We continue to believe in significant potential opportunities in Alzheimer’s disease and depression, two large therapeutic areas with great unmet need.” 1. American Stroke Association. 2. 2018 AHA guidelines on management of ischemic stroke. 3. Free cash flow defined as net cash flow from operations less capital expenditures. 4. aaic.alz.org/downloads2020/2020_Race_and_Ethnicity_Fact_Sheet.pdf . 5. Lupus Foundation of America www.lupus.org/resources/lupus-facts-and-statistics.